Axial-flow pumps use centrifugal force to separate immiscible fluids, or solids within a fluid carrier, by specific gravity and have impellers that direct the flow of fluid axially. Axial-flow pumps can be configured to separate solids within a water carrier into three separate streams by specific gravity: a lighter than water solids stream, a heavier-than-water solids stream, and water. Amos Broughton in U.S. Pat. No. 4,834,887 describes an axial-flow pump with three output streams. A special type of axial-flow pump was developed by Harvey Richter and described in U.S. Pat. No. 5,084,189 (hereafter, “Richter's separator”). Richter's separator utilizes an impeller with a hollow core. The hollow core occupies the central axis of the impeller and passes fluid from the device inlet. The impeller includes two or more helical blades having decreasing axial pitch in a direction of fluid flow. Because Richter's impeller is hollow in the center, it does not have a central shaft to drive it. Instead, Richter's impeller is driven by a rotating drum attached along the outer circumference of the impeller.
Enviro Voraxial Technology Inc. (EVTN) sells devices that are based on the principles of Richter's separator and sold under the registered trademark “Voraxial.” EVTN, as well as others, have disclosed separators that are based on the principles of Richter's separator that separate immiscible fluids, or solids within a fluid carrier, into three components by specific gravity: a lighter-than-water, equal to water, and heavier-than-water. The lighter-than-water component is discharged through a hollow tube with at least an inlet portion axial to the center of the hollow impeller. EVTN's three-output Richter-type separators have primarily been used to separate oil from water and from heavier-than-water components such as sand or grit. Typical applications of the three-output Richter-type separators include oil spill cleanup, oil extraction, and oil/petroleum processing operations.